The major emphasis will be the continuation of ongoing studies to characterize the discriminative stimulus properties of narcotic agonists and antagonists in the rat and squirrel monkey. The governing hypothesis is that the components of action of narcotic agonists and antagonists that enable them to function as discriminative stimuli in animals are analogous to the components of action that engender subjective effects in man. Thus, drug discrimination paradigms could provide animal models for the pre-clinical identification and evaluation of the components of action of opioids that underlie their abuse potential. Independent groups of rats will be trained to discriminate between saline and either 1.0, 3.0 or 10 mg/kg of morphine. Stimulus generalization (i.e., dose-response) curves for novel drugs will be determined and compared across groups as a function of the morphine training dose. Another group of rats will be trained to concurrently discriminate among saline, morphine (3.0 mg/kg) and cyclazocine (0.3 mg/kg) in order to assess more directly the morphine-like and cyclazocine-like discriminative stimulus properties of drugs with mixed agonist and narcotic antagonist properties. Finally, discriminative stimulus properties of mixed agonist-antagonists will be evaluated in squirrel monkeys trained to discriminate between saline and pentazocine (3.0 mg/kg).